Marine and Freshwater Resources Institute Report No. 39
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Marine and Freshwater Resources Institute Report No. 39 Seagrass Mapping of Port Phillip Bay Sean Blake and David Ball June 2001 Marine and Freshwater Resources Institute Report No. 39 Seagrass Mapping of Port Phillip Bay Sean Blake and David Ball June 2001 Marine and Freshwater Resources Institute PO Box 114 Queenscliff 3225 © The State of Victoria, Department of Natural Resources and Environment, 2001 This work is copyright. Apart from any use under the Copyright Act 1968, no part may be reproduced by any process without written permission. ISSN: 1328-5548 ISBN: 0 7311 4995 5 Copies available from: Librarian Marine and Freshwater Resources Institute PO Box 114 Queenscliff VIC 3225 Phone: (03) 5258 0259 Fax: (03) 5258 0270 Email: [email protected] Preferred way to cite this publication: Blake, S. and Ball, D. (2001). Victorian Marine Habitat Database: Seagrass Mapping of Port Phillip Bay. Geospatial Systems Section, Marine and Freshwater Resources Institute Report No. 39. Marine and Freshwater Resources Institute: Queenscliff. General disclaimer: This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Seagrass Mapping of Port Phillip Bay CONTENTS List of Figures ........................................................................................................ ii List of Tables.......................................................................................................... ii List of Historical Photographs.............................................................................. ii List of Appendices ................................................................................................ iii SUMMARY............................................................................................................1 1. INTRODUCTION ............................................................................................2 1.1 Objectives................................................................................................2 1.2 Seagrass...................................................................................................2 1.3 Port Phillip Bay.......................................................................................3 1.4 Seagrass Species in Port Phillip Bay.......................................................5 2. MAPPING THE SPATIAL DISTRIBUTION AND DENSITY OF SEAGRASS IN PORT PHILLIP BAY...........................................................7 2.1 Survey Methods.......................................................................................7 2.1.1 Remote Sensing of Shallow Marine Environments.....................7 2.1.2 Photography Specifications........................................................7 2.1.3 Aerial Photography Interpretation.............................................7 2.1.4 Field Verification Process ..........................................................7 2.1.5 Field Classifications ...................................................................9 2.2 Results of Mapping................................................................................15 2.3 Discussion..............................................................................................17 2.4 Assessment of Mapping.........................................................................19 3. AN ASSESSMENT OF SEAGRASS CHANGES IN PORT PHILLIP BAY.................................................................................................21 3.1 Previous Studies ....................................................................................21 3.1.1 Bay-wide Studies.......................................................................21 3.1.2 Site-specific studies...................................................................22 3.2 Comparison of Previous Studies with 2000 Mapping...........................24 3.3 Assessment of Seagrass Changes from Historical Aerial Photography 30 3.3.1 Selection of Study Sites and Aerial Photography .....................30 3.3.2 Scanning and Geo-registration of Historical Aerial Photography ..............................................................................30 3.3.3 Results.......................................................................................31 3.3.4 Observations from Historical Aerial Photography ..................31 3.3.5 Summary of Observations from Historical Aerial Photography ..............................................................................33 3.4 Overview of Assessing Seagrass Changes with Historic Aerial Photography...........................................................................................34 4. GENERAL DISCUSSION AND FINDINGS ...............................................38 ACKNOWLEDGMENTS ...................................................................................39 Marine and Freshwater Resources Institute – Page i Seagrass Mapping of Port Phillip Bay REFERENCES.....................................................................................................40 LIST OF FIGURES Figure 1.1 Port Phillip Bay location map Figure 2.1 Specialised survey vessel with semi submersible pod lowered Figure 2.2a Ground-truthing transects and points recorded in Port Phillip Bay Figure 2.2b Example of how the fieldwork transects were used to classify the mapping derived from aerial photography. Figure 2.3 Seagrasses of Port Phillip Bay Figure 2.5 Areas of individual seagrass categories as a percentage of the total area of seagrass mapped in Port Phillip Bay Figure 3.1a Seagrass distribution in Port Phillip Bay, 1957, 1962-63 Figure 3.1b Seagrass distribution in Port Phillip Bay, 1968-70 Figure 3.1c Seagrass distribution in Port Phillip Bay, 1978-81 Figure 3.1d Seagrass distribution in Port Phillip Bay, 2000 Figure 3.2a Area of seagrass cover as a percentage of total study area at Grassy Point Figure 3.2b Area of seagrass cover as a percentage of total study area at Sands Caravan Park site, Leopold Figure 3.2c Area of seagrass cover as a percentage of total study area at Altona Figure 3.2d Area of seagrass cover as a percentage of total study area at Blairgowrie Appendix 3 Figure 2.4 Seagrass map index Appendix 3 Figures 2.4a-p Maps of seagrass distribution in Port Phillip Bay LIST OF TABLES Table 2.1 Seagrass and macroalgae species and density and substrate classification categories recorded during the field survey Table 2.2 Summary area statements for seagrass and macroalgae categories recorded in Port Phillip Bay Table 2.3 Results of a points-in-polygons analysis - groundtruthing versus seagrass polygons. Table 3.1 Areas of seagrass recorded in Port Phillip Bay (Bay-wide studies) Table 3.2 Results of historic studies compared to present study Table 3.3 Historical aerial photography used to identify changes in seagrass distribution at specific sites in Port Phillip Bay LIST OF HISTORICAL PHOTOGRAPHS – APPENDIX 2 Photo 3.1a Grassy Point, 1947 (Scale 1:10,000) Photo 3.1b Grassy Point, 1975 (Scale 1:10,000) Photo 3.1c Grassy Point, 1992 (Scale 1:10,000) Photo 3.1d Grassy Point, 2000 (Scale 1:10,000) Photo 3.2a Sands Caravan Park, Leopold, 1974 (Scale 1:10,000) Photo 3.2b Sands Caravan Park, Leopold, 1984 (Scale 1:10,000) Photo 3.2c Sands Caravan Park, Leopold, 1993 (Scale 1:10,000) Marine and Freshwater Resources Institute – Page ii Seagrass Mapping of Port Phillip Bay Photo 3.2d Sands Caravan Park, Leopold, 2000 (Scale 1:10,000) Photo 3.3a Altona, 1962 (Scale 1:10,000) Photo 3.3b Altona, 1979 (Scale 1:10,000) Photo 3.3c Altona, 1993 (Scale 1:10,000) Photo 3.3d Altona, 2000 (Scale 1:10,000) Photo 3.4a Blairgowrie, 1966 (Scale 1:10,000). Photo 3.4b Blairgowrie, 1993 (Scale 1:10,000). Photo 3.4c Blairgowrie, 1996 (Scale 1:10,000). Photo 3.4d Blairgowrie, 2000 (Scale 1:10,000). LIST OF APPENDICES Appendix 1 Seagrass GIS Layer Metadata ......................................................... A1 Appendix 2 Port Phillip Bay Historical Aerial Photography............................ A10 Appendix 3 Port Phillip Bay Seagrass Maps.................................................... A19 Important Note on Seagrass Species Definition The two species of Zosteraceae observed in Port Phillip Bay; Heterozostera tasmanica and Zostera muelleri, cannot be differentiated by the remote sensing techniques employed in this study and have been grouped into a single category of “Zostera/Heterozostera”. Marine and Freshwater Resources Institute – Page iii Seagrass Mapping of Port Phillip Bay SUMMARY This study forms part of a state-wide program by the Department of Natural Resources and Environment (NRE) to map and characterise the distribution of seagrass communities throughout Victoria. The objectives of the study were to map the distribution of the different seagrass species found in Port Phillip Bay and to compare the present distribution with that observed in previous studies. The mapping method involved acquiring high quality aerial photography, interpreting the aerial photography to identify seagrass areas, ground-truthing these areas in the field, digitising seagrass areas with a GIS and adding seagrass species and density attributes for each area based on the field data. The fieldwork was primarily undertaken by running transects with a specialised survey vessel